1. Field of the Invention
The present invention relates generally to a cassette for use in recording and reproducing devices and more specifically to a cassette which is arranged to provide accurate tape end detection, which is simple in construction and which can be made of a brightly coloured material.
2. Description of the Prior Art
In a previously proposed cassette arrangement such as shown in FIG. 1, in order to detect the end of the tape being approached it has been proposed to add a transparent leader tape section to each end of the magnetic tape and arrange for a light source "e" to be introduced into the cassette, and dispose light responsive sensors "g" in positions wherein, when an end of the tape is being approached and the leader tape at that end begins to unwind from one of the two tape reels, the light from the light source "e" is able to pass through the transparent leader tape, pass out through a light transmission aperture "b" and be received by one of the sensors or pickups "g".
With this arrangement it is possible to timely stop the motor mechanism which drives the tape reels prior the actual end of the tape being completely reached and avoid damage to or breakage of to the tape due to the continued application of torque to the take up reel when the tape has been completely wound thereonto.
However, this arrangement has suffered from the drawback that erroneous detection of the tape end tends to occur and result in the operation of the tape drive being stopped prematurely. The reason for this erroneous detection has been found to be due to light, which enters the cassette such as through the window section, provided for visually ascertaining how much tape is wound on each reel, is sometimes reflected on the internal structure of the cassette and/or the magnetic tape and a light ray such as denoted by "d" is directed toward one of the light transmission apertures "b" formed in the side wall of the housing. This light ray propagates along a path sufficiently close to line "f" (along which the light beam emitted from the light source "e" is transmitted) to be received by a sensor "g" in a manner that triggers an erroneous tape end signal.
In order to overcome this problem it has been proposed in JP-A-57-26779 to, in addition to the common technique of making the cassette case of a dark coloured material which exhibits low reflectivity, form one or more portions of the window section through of the cassette case of a semi-transparent material in an effort to diffuse the light entering the interior of the cassette.
In JP-A-60-236177 it has been proposed to provide the upper surface of the lower flange of the tape reels with mat surfaces in order to reduce the amount of light which is reflected thereoff.
However, neither of these arrangements has proven sufficiently satisfactory.
In JP-A-60-102787 it has been proposed to add a so called "lock plate" arrangement to the cassette. This arrangement includes a "tunnel" section through which the light which reaches the sensors or pick-ups must pass. However, this construction has suffered from the drawbacks that the length of the tunnel sections must be quite long in order to adequately screen out the reflected light rays which will induce erroneous tape end signals and thus obviates its use in smaller type cassettes wherein sufficient space is not available. Further, this arrangment due to its disposition and orientation cannot be formed integrally with the cassette and must be added as a separate unit. Installation of the unit must be made carefully so as to ensure proper operation. This of course adds to the number of assembly operations and therefore to the cost of the device. In addition to this, the lock plate member itself requires the inclusion of a metallic slide member which further increases the production costs.